In circuit pattern formation, a semiconductor wafer, if desired with its thickness adjusted by back side polishing, is cut into chips (dicing step), and the separated chips thus formed are fixed to an adherend such as a lead frame with an adhesive (mounting step) and then subjected to a bonding step. After the dicing step, the semiconductor wafer is usually cleaned at an appropriate liquid pressure, generally about 2 kg/cm.sup.2, to remove the offcut, etc.
Where an adhesive is separately applied to a lead frame or the chip in the treatment step, it is difficult to uniformly apply the adhesive, and the application of the adhesive needs a special apparatus and much time. Therefore, a dicing-die bonding film which adheres and supports a semiconductor wafer in the dicing step and also provides an adhesive layer for chip fixing in the mounting step has been proposed as disclosed in JP-A-60-57642 (corresponding to U.S. Pat. No. 4,961,804) (the term "JP-A" as used herein means an "unexamined published Japanese patent application").
The dicing-die bonding film proposed comprises a substrate having provided thereon a releasable electrically conductive adhesive layer. After a semiconductor wafer is cut into chips while being supported by the adhesive layer of the dicing-die bonding film, the substrate is stretched to release the chips along with the adhesive layer. The individual chips with the adhesive layer are then picked up and fixed to an adherend such as a lead frame via the adhesive layer.
It is required for a film of this type to exhibit satisfactory holding power for supporting a semiconductor wafer and satisfactory release properties so that the chips may be released together with the electrically conductive adhesive layer. However, it has never been easy to satisfy these two requirements in good balance. Where, in particular, a high holding power is needed as in a dicing system using a rotary wheel cutter, it has been difficult to obtain a film having such a high holding power in good balance with the release properties.
In order to overcome this problem, various improvements have been proposed to date. For example, JP-A-2-248064 proposes a film having an ultraviolet-curable pressure-sensitive adhesive layer between a substrate and an adhesive layer. The ultraviolet-curable layer is cured by ultraviolet irradiation after dicing to reduce its tack to the adhesive layer so that the chips may be released with ease. However, the film is still unsatisfactory in maintaining a balance between holding power during dicing and release properties after the dicing. For example, large-sized chips as larger than 10 mm.times.10 mm could not easily be picked up with a general die bonder.